Switched-mode power supplies (SMPS) are commonly used and increasingly replacing “classical” power supplies composed of a transformer and a linear voltage regulator. SMPS use switching power converters to convert one voltage (e.g., an AC line voltage or a 13.8 V battery voltage) into another voltage, which may be used as supply voltage for an electric device or an electronic circuit. For example, switching power converters are widely used to charge batteries of mobile devices such as mobile phones, portable computers, portable electric drills, etc. Many different switching power converter topologies are known in the field, such as buck converters, boost converters, Ĉuk converters, flyback converters, etc.
For safety reasons, it may be desirable that the power converter circuit includes galvanic isolation from between the input circuit (connected to the utility power grid) and the output circuit (providing the desired output voltage to a load). Usually, optocouplers are used to galvanically isolate a feedback signal representing the regulated output voltage from the input circuit of the power converter circuit. The power conversion is accomplished by using a transformer (included e.g., in a flyback converter). However, when a car battery is used as input voltage source (instead of the power grid) the galvanic isolation may be optional or even undesired.
The switching operation of a switching converter is controlled by a controller which may be optimized for a specific switching converter output voltage and for a specific range of input voltages. Dependent on the actual application it may be desirable to adjust the switching converter output voltage or the output power, and, when changing, e.g., the switching converter output voltage, the mentioned controller may operate in a sub-optimal (inefficient) state. Also the loop stability can be impacted by changing significantly the output voltage range. Furthermore, protection features such an over-voltage protection may be inoperative or not working properly in such sub-optimal state. Thus there is a need for improved switching converters which are able to efficiently provide stable output voltages of different nominal values.